Since updating to Firefox 87.0 I've been unable to log in to Trello.
To reproduce:
1. At https://trello.com/login I enter my email address
2. The login button changes to "Login with Atlassian". Click on that.
3. id.atlassian.com screen briefly appears and then it redirects back to the trello.com/login screen
4. Go back to step 1
Alternative, in step 1 click on "Continue with Google" using same email address. Same redirect sequence/loop occurs.